This grant deals with attempts to chemically define the relationship between the structure and function of chromatin in eukaryotic cells, and contains the following major projects which are in progress: 1. Purification of the nuclear histone acetylase from calf thymus. 2. Substrate selection by the purified histone acetylase enzyme. 3. The mechanism of action of n-butyrate in increasing histone acetylation. 4. Characterization of nucleosome-like particles formed between histones and single-stranded DNA. 5. An electron microscopic investigation of altered chromatin structure in active genes. In addition, attempts are being made to determine the cell and molecular basis of positional information, using as model systems the signalling in the chick limb bud by cells of the ZPA, and the pattern of differential RNA transcription in early embryos of Drosophila.